Oehler Skyscreen III to AVR

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Oehler Skyscreen III to AVR

Postby GoBO207 » May 23rd, 2012, 7:33 pm

Hi all,

I'm looking at interfacing these Skyscreen III sensors with an AVR. First I will post some pictures to see if anyone recognisances the component used in the sensors.

The sensor appears to be a photo transistor sort of thing, Motorola part number SRD461 8339 (Note the 3rd leg that appears to be cut off). See the photos attached. The model of the Chronograph is an Oehler model 33.

So far I have worked out 2 pins going to the main uC that go high when something passes through it. Each pin corresponds to a sensor. So the plan is to have the first sensor save the timer value on an interrupt to the pin. Then have an interrupt for timer overflow to record how many times the timer has reset back to zero, then an interrupt to record the timer value as the second sensor goes high. All this on the 16bit timer going at 20Mhz. All thats left is a simple calculation and it can spit out the result. The issue im having is with the calculations as I am not familiar with what the AVR can do with floats etc.

But the point of this post is to help out a guy on a recent article. If anyone know how these sensors work, or where to get a new SRD461 (I popped 1, oops) please reply.

Cheers,
GoBO207

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Note the 3rd leg that appears to have been cut off.
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To view, 2 leads going into the die, and 1 for the case I assume.
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The circuit to detect the projectile going through the sensors. It will put a pin high for each sensor when it detects something.
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GoBO207
 
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